1. Field of the Invention
The invention relates to apparatus for truncating continuously formed tubes, such as tubes of cellulosic material.
2. Description of Material Information and Pertinent Materials
Cardboard tubes are conventionally manufactured by winding a plurality of strips of paper or cardboard helically on a machine known as a "spiraler". A known machine for accomplishing this comprises a fixed cylindrical mandrel on which one or more strips are helically wound. The spiral edges of the strips form predetermined angles with the axis of the mandrel. If more than one strip is used in forming the tube, the strips are connected in series by glueing an end of one strip to an end of another strip so as to form a continuous band of desired length for wrapping around the mandrel. The tube so formed is simultaneously rotated and longitudinally translated by an endless conveyor belt effecting a dead turn around the tube.
As a continuous tube of cardboard is formed, it is truncated into individual tubes at a cutting or truncating station. Conventional truncating apparatus normally is operated in a cyclical manner. Actuation of the cutters is synchronized to the velocity of advancement of the tube formed relative to the length of the truncated portions to be obtained.
Obviously, it is necessary for the cutters to follow the tube during truncation for a certain time period so as to obtain a cut along a vertical section, i.e., along a plane perpendicular to the axis of the tube. Certain known systems to accomplish these ends comprise a cutter in the form of a circular saw mounted on a movable carriage, and a means for thrusting the saw, in a direction transverse to the longitudinal movement of the tube, into contact with the tube. The action of the saw and the movement of the carriage are controlled in a manner such that the saw penetrates transversely into the tube at the desired moment while following longitudinal movement of the tube during cutting action of the saw.
Another known system controls a saw in a cyclical, rotating movement such that the period of movement is a function of the velocity of advancement of the tube and the length of the truncations to be obtained, so that longitudinal movement of the saw occurs during cutting at substantially the same velocity as the advancement of the tube.
However, these known saw apparatus suffer from numerous disadvantages with respect to the quality of the cut. In this regard, a clean cut is often difficult to obtain. Thus, the end of the tube may have rough edges or burrs. As a result, excessive saw dust is produced. Moreover, such saws are dangerous because they are positively driven and can be activated at times when there is no work to be cut.
In an attempt to overcome these problems, high performance systems, using circular knives, that cooperate with a support mandrel positioned within the cardboard tube, have been used with some success. Such systems make it possible, during each cycle of operation, to cut one or more tube portions along a straight (vertical) cross-section, and obtain essentially smooth edges which are practically free of burrs.
Conventional knife cutting systems generally comprise three elements:
(a) a support and guide elements for the cardboard tube in the form of cylindrical rollers and wheels; PA1 (b) a cylindrical support mandrel, generally of very hard material, positioned within the tube; and PA1 (c) cutting knives or saws in the form of disks which are attached onto rigid or elastic supports.
The above three types of elements (a), (b), (c) are operatively interconnected. As such, one or more of these elements is moved along the axis of rotation so as to result in truncation of a tube at the moment of penetration of the knives into the wall of the tube. During truncation, all of the elements are longitudinally displaced at a velocity synchronized with longitudinal advancement of the tube.
This displacement, or shifting movement, may be achieved by electrical, hydraulic, pneumatic, or equivalent activating means whose action is adjusted proportionally either to the velocity of operation of the feed means for the tube, or to the velocity of the unwinding of the strips of paper or cardboard.
Providing the tube with a reference element is sometimes used as part of a system for coordinating the movement of these means. In such instance, a reader follows this reference element in a manner so as to sense and send information to a control element of the activation means which coordinates the displacement.
In addition, hydraulic, pneumatic, mechanical or electric activation means may also be used to effect the penetration of the knives into the tubes until they meet the support mandrel.
Thus, all of these systems are complex, costly and of dubious safety and reliability.